Distribution and storage of soil organic carbon in a coastal wetland under the pressure of human activities

Purpose: Soil organic carbon (SOC) stock is one of the most important carbon reservoirs on the earth and plays a vital role in the global climate change. However, research on the carbon sequestration and storage of coastal wetland soil is very scarce. Therefore, a study in the coastal wetland was conducted to investigate the SOC distribution, storage, and variation under the influence of human activities. Materials and methods: Surface soil samples in different seasons and profile soil samples were collected in the Changyi coastal wetland. SOC content, soil physicochemical properties, and sedimentation rate were determined. Organic carbon storage and burial flux were calculated. On the basis of correlation analysis and comparative study, factors affecting the distribution and storage of SOC were investigated. Results and discussion: The average SOC content of the surface soil in June and November was 4.65 and 6.13 g kg⁻¹, respectively. The distribution of surface SOC content was consistent with the distribution of vegetation and was affected by the soil particle size. In plant-covered area, the relationship between SOC content and depth could be expressed by the power function y = ax^b. The contribution of plants to SOC was only significant in the shallow layer. As for the deep layer, the SOC content was higher in the mudflat. The organic carbon storage in the upper 1 m soil was estimated at 1.795 kg m⁻² in average and the total organic carbon storage of Changyi wetland was estimated at 6.373 × 10⁷ kg. The sedimentation rate was very low and the average organic carbon burial flux of the whole wetland was 17.5 g m⁻² a⁻¹. Conclusions: Low sedimentation rate, weak downward migration, and high decomposition rate of organic matter caused by poor hydrological condition were the reasons why the SOC storage in Changyi wetland was low. Under intensive human activities, the Changyi wetland was drying and the organic carbon storage was reducing. Strategies were proposed to be taken urgently to restore the wetland for the long-term benefit.